[client][buttonsmanager] create empty manager file
[client][buttonmanager] base structure
[client][buttonmanager] implement outer button creation
[client][buttonmanager] enable ranking when creating buttons
[client][buttonmanager] can set attributes on created button
[client][buttonmanager] implement inner buttons
[client] define sidebar buttons with the new buttonmanager
Merge pull request #158 from Paulloz/buttonmanager

Fixes #130